function [ Dx ] = getDx( i,j,U,V,NJue,NIue,NJut,h )

% Right and left volumes
U_cen   = U ( Umap (i  ,j  ) );  % center of finite volume
U_right = U ( Umap (i+1,j  ) );
U_left  = U ( Umap (i-1,j  ) );

% Top and bot volumes, considering ghost nodes

if ( j==1 ) U_bot = - U_cen ; else U_bot   = U ( Umap (i  ,j-1) ); end
if (j<=NJue)
    if ( j==NJue && i<=NIue ) U_top   = - U_cen; else U_top   = U ( Umap (i  ,j+1) ); end
else
    if ( j==NJut ) U_top   = - U_cen; else U_top   = U ( Umap (i  ,j+1) ); end
end

Dx  = U_left + U_right + U_top + U_bot - 4 * U_cen;

Dx  = Dx/h^2;

end

